My backyard design needs some critiquing!

I recently bought a house and am going to start with the backyard for landscaping. Im not sure if we are going to do it all at once or in phases but here are a few things I want to have here. There is alot of space so that should not be an issue.

-Large Pond
-Firepit and patio area
-Low voltage lighting

I was doodling and this actually came out kinda like i wanted. But a few questions i have.

-How do you guys drain sunken patios (below grade), i would suspect a drain tile but where do you place the drains with a firepit in the middle?

-For the deck, it originally has a 3x3 set of stairs directly on along the house. Instead of tearing down the deck, i found the steps are just a set so I could take those down and build a set spanning almost the whole side. Good idea?

-For the top patio i stayed a couple feet away from the house w/ a planting buffer, Good idea?

- The double lines on the patios are sitting walls

- Im going to knock down the timber wall along the deck and build a rock wall further out

Heres a couple pics to give an idea

Let me have it with any comments or things you dont like or need to be addressed. Price is not much of a concern but should be within reason